The present invention generally relates to a system for monitoring and controlling the operation of a web printing press and for providing superior operating efficiency and an operating history database. The system includes the capability of acquiring digitized images of predetermined areas printed patterns of ink and analyzing the images to determine reflective density and register misalignment and for generating control signals to make any necessary density and register corrections.
Web printing presses of the type which print full color magazines and other printed material at high speeds generally have a number of printing stations, each of which prints a different color on the web as the web passes through the press. Such presses generally have multiple printing stations which generally print the colors cyan, magenta yellow and often two other colors in addition to black. The quality of the printed matter is a function not only of the proper registration of each of the colors by the respective printing stations, but also by the amount of ink and its resultant pattern of distribution that is printed for each color by the printing stations.
The distribution of ink that is transferred to the web during a printing operation is fundamentally controlled by a number of ink zone control mechanisms, commonly referred to as xe2x80x9ckeysxe2x80x9d that are spaced across the width of the printing press, typically at approximately every 1 to 2 inches, depending upon the press type, and these keys effectively determine zones that regulate the amount of ink that is available to be ultimately transferred to a web. For each color that is being printed, there may be very little or a relatively large amount of ink transferred at each key location of each printing station, depending upon the perceived color in the image that is printed. As is well known to those skilled in the art, a woman in a bright red dress that takes up a significant portion of the area of an impression would require a larger amount of magenta and yellow ink being applied at the magenta and yellow printing stations, since red is a combination of magenta and yellow. The keys in the area of the red dress would be controlled to provide more of such ink than in other areas of the impression being printed. As a general matter, the transfer of the ink being printed at each printing station is important to achieve the desired perceived color in the resulting product.
It has long been a practice in the operation of full color printing presses to print certain test targets of each color of ink in a test print area within an impression (such as pages of a magazine) for the purpose of qualifying the quality of the final finished product by measuring the reflective density of the final printed product using a small hand-held densitometer. Such densitometers give readings that range from approximately 0.5 to 2.5 with the larger number being substantially reduced reflectivity, i.e., black. Such densitometers are quite sensitive in their operation and must often be calibrated to give reliable reflective density readings. After a printing job has been set up, pressmen must take samples at periodic intervals during a press run and perform reflective density measurements to insure that the transfer of ink has not changed. If it has, then they make appropriate adjustments to the press to bring the measurements into conformance. It is also known in the art that adjustment of the press does not result in an immediate change in the transfer of ink. For example, adjustment of one ink key may have an effect on adjacent keys.
In our prior U.S. Pat. No. 6,058,201, there is described an extremely sophisticated system for generating dynamic reflective density measurements for a web printing press, which system acquires digitized images of particular web targets that are located in the test print area between adjacent impressions. Since the size of the test print area between adjacent impressions represents an area of wasted paper, modern presses continue to decrease the size of the test print area to minimize waste. With the test print area size becoming ever smaller, the targets that are used for densitometer measurements and also register control must necessarily be smaller. The compression of the test print area size also decreases the space between the targets and the actual printed matter which creates an increased technological challenge to providing a system which will reliably operate.
Modern presses are also becoming larger in the sense that they print a wider web which must then be slit into multiple ribbons in the longitudinal direction and then be converged to form a multi-layer composite product that is ultimately cut in the transverse direction to form magazines and other print material. Because of the increased width of the web, registration through the various print stations may vary across the web so that control of the registration on a key-by-key basis is necessary to achieve an acceptable printed product. Because of the flexibility and elasticity of the web, it is possible to introduce a small roller, push member or the like into contact with the narrow portion of the web to buckle that portion of the web and vary its path length relative to the remainder of the web and thereby accomplish register control on less than a web width basis and even on a key-by-key basis.
Many modern press installations have a complete complement of accessory control apparatus, including a web guide at the input of the web, a registration control mechanism, a color density measurement and adjustment apparatus, a ribbon slitting and converging mechanism, as well as a web guide at the upstream end of the same, and web break detectors that are adapted to shut down the press in the event of a web break. Overall control of all of these mechanisms and apparatus is highly desirable to achieve a reliable and efficient press operation.
Accordingly, it is a primary object of the present invention to provide an improved system for dynamically monitoring and controlling a web printing press, including apparatus for measuring and controlling reflective density as well as registration of print operations, in addition to monitoring and controlling other auxiliary equipment such as the ribbon slitting and converging apparatus.
It is another object of the present invention to provide such an improved system which includes a process manager that is adapted to provide the above apparatus with preset values that enables the press to be controlled whereby make ready operations are quickly accomplished which increases the operational efficiency of the press and concomitantly reduces waste.
Yet another object of the present invention is to provide such an improved system that includes a process manager which interfaces all of the apparatus that operate the press, receives job information from a printing company""s pre-press department which is downloaded into the process manager, and generates the preset values for all of the apparatus for carrying out the printing job.
Still another object of the present invention is to provide such an improved system that enables registration to be reliably obtained even though the target pattern used to do so is extremely small and the test print area between successive impressions is extremely small.
A corollary object lies in the provision for obtaining of relatively close registration through use of the presets generated by the process manager and the use of a predetermined register target pattern printing at a specific location. This then enables the color density apparatus to reliably print the various color block sets in the test print area and be reliably located, acquired and analyzed.
Yet another object of the present invention is to provide such an improved system which has two or more target blocks at each key location across the width of the web which enables registration to be independently measured on a key-by-key basis so that accurate registration control can be achieved across the entire web.
A more specific object of the present invention is to provide such an improved system which determines and controls registration of the various print stations by initially using a register target pattern that is preferably printed in the test print area at the center line of the press, which when its digitized image is acquired, enables the apparatus to reliably acquire the image of each of a plurality of other color block sets located in the test print area along the width of the web for the purpose of determining color density. A corollary object lies in the provision for using such block sets for controlling registration at each key location on a continuing basis during a press run.
Other objects and advantages will become apparent upon reading the following detailed description, while referring to the attached drawings, in which: